This invention relates to a device for determining the amount of air mixed into a hydraulic circuit of a hydraulic device such as a vehicle hydraulic brake device and producing an alarm if necessary. More specifically, it relates to a mixed air amount alarm device which can prevent an alarm from being cancelled when an alarm should be produced, due to fluctuation in the air amount (volume) resulting from temperature change, and which also can stop a warning when it returned to a safe state due to spontaneous discharge of air out of the hydraulic circuit.
The present applicant proposed in JP patent application 2002-108160 a soundness evaluation method for a hydraulic pressure control unit which makes it possible to determine the air amount in a hydraulic circuit (piping) provided in a hydraulic device such as a hydraulic brake device, and to produce an alarm if the air amount is determined to be excessive.
With this soundness evaluation method, a first pressure detecting means is connected to piping connecting a hydraulic pressure control means to a hydraulic device to detect the hydraulic pressure in the piping with the first pressure detecting means, and further, a second pressure detecting means is connected to an accumulating means for accumulating hydraulic pressure generated by a hydraulic pressure generator to detect the hydraulic pressure in the accumulating means, and a control device for recognizing the detection signals from the first and second pressure detecting means determines a stationary state when the absolute value of pressure gradient of the accumulating means per unit time when the hydraulic pressure control means outputs hydraulic pressure becomes equal to or lower than a predetermined amount.
The decreased amount (i.e. discharge amount) of hydraulic pressure of the accumulating means from the time before the hydraulic pressure control means is activated until the abovementioned normal state, and the hydraulic pressure in the piping at the stationary state are determined, and they are compared with the values in the normal state during which no air is mixed in the piping. If the amount of air in the piping increases, the relation between the amount of fluid QW discharged from the accumulator and the output hydraulic pressure PW differs from the relation in the normal state. Thus, it is possible to judge the amount of air in the piping from how the relation between the fluid amount QW and the hydraulic pressure PW measured in the stationary state shifts from the relation in the normal state and produce an alarm when a shift occurs that exceeds a preset value.
The amount of air in the hydraulic circuit is the volume of air. The volume of a gas varies with the temperature even though the mole amount is constant (Boyle-Charles' law).
Thus, in the above soundness evaluation method, if the fluid temperature rises, since the volume of air expands, it is determined that the air amount is excessive. But when the fluid temperature lowers, the air amount is not determined to be excessive. Thus, confusion occurs because an alarm is sometimes given and sometimes not given. Besides, that an alarm is not produced in spite of the fact that it is known that when the fluid temperature rises, an alarm will be produced is a state in which is hidden danger in a vehicle brake device. This is not preferable. In other words, producing an alarm in this state is not a false alarm, but can be said to be a desirable measure.
One object of this invention is to eliminate these disadvantages, and not to cancel an alarm if the air amount is determined to be excessive in a state of expanded air due to temperature rise and thereafter the determination of excessive air amount is not met due to cooling.
A second object of this invention is to make it possible to stop an alarm if air amount in the hydraulic circuit has decreased due to spontaneous release, and as a result, a safe state is recovered in which no air amount excessiveness occurs even if the fluid temperature becomes high.